Force Fields and Plasma Shields

Space-borne protective energy systems, like the deflector shields on the fictional starship U.S.S. Voyager, are on the drawing board of real-world scientists.

These "cold plasmas" -- analogs to the sophisticated defensive grids envisioned by Star Trek's creators -- are ambient-temperature, ionized gases related to those found deep within the sun's core.

Such plasmas are capable of shielding satellites and other spacecraft, making them invisible to radars, or both. Nor will they fry electronics or melt metal.

On Earth, cold plasmas should permit rapid, room-temperature sterilization of food, medical equipment and contaminated civilian and military gear. Low-temperature plasmas could one day also make possible an entire new generation of miniature lasers and ultra-low-energy fluorescent light tubes.

While scientists have known of low-temperature plasmas since at least the end of the 19th century, only within the past several years have techniques emerged to make cold plasma generation practical.

Vaulting to the first ranks of cold-plasma research in the last three years has been soft-spoken, unassuming Tunisian native Mounir Laroussi, an electrical and computer engineer at Old Dominion University in Norfolk, Virginia. Research groups at Stanford, Princeton, Ohio State, Wisconsin and New York Polytechnic also are conducting their own plasma-research programs.

Side view of a cold plasma inside a Pyrex glass container. Cold plasmas can cloak satellites and spacecraft from radar view and shield them against attack from certain kinds of energy weapons.

Laroussi has literally put plasma on the table: devising an apparatus that creates a mini-plasma inside a Plexiglas cube by passing an electric current through helium gas via specially calibrated electrodes.

Laroussi's process, specified in pending patent applications, is scalable; cold-plasma containers of virtually any size are feasible. No vacuum pumps are required, since the plasma is generated at normal atmospheric pressure.

"Mounir is on the forefront. He's one of the pioneers," said Igor Alexeff, president of the Institute of Electrical and Electronics Engineers' Nuclear and Plasma Sciences Society and professor emeritus of electrical engineering at the University of Tennessee in Knoxville. "He's pushing very hard to develop a variety of practical plasmas. His work is pretty impressive."

Invulnerable and invisible
The U.S. Air Force allocates some $10 million a year for research geared toward satellite protection. Of that amount, $2 million is dedicated to low-temperature plasma studies.

Robert Barker, program manager for plasma physics in the Air Force's Office of Scientific Research in Arlington, Virginia is so taken with Laroussi's approach that he thus far has funneled $250,000 into Laroussi's research since his arrival at Old Dominion from the University of Tennessee a little over a year ago. The Air Force has supported Laroussi's work since 1996.

Barker is drawn not just by Laroussi's plasma-creating prowess, but his ability to make low-temperature plasma inexpensively, in bulk and without the need for hulking equipment.

"What's intriguing about Mounir's work is the large volumes of plasma he's been able to generate," Barker said. "He's making very good progress in keeping costs and weight low. His approach gives the best power figures for practical, large-volume generation of cold plasma we have to date."

Power-hungry plasmas
Poke a finger inside Laroussi's tabletop plasma-generating apparatus and all you'll get from the bluish, pilot-light-like ionized gas is a slight tingle. But the harmless sensation is misleading, since it doesn't give a complete picture of plasma's power. Depending on how a plasma is "tuned," or how it is made more dense by increasing its frequency, it could ward off microwave bursts and discharges from ground-based, energized sources of potential damage and disruption.

Swirling in and around one another, a plasma's charged particles interact constantly, giving rise to localized attractions or repulsions. External energy splashing against the plasma --- say, from a potentially disabling, concentrated burst of microwaves, or perhaps even from certain varieties of particle-beam weapons fired from military bases on Earth -- could be caught up within the plasma's complex electromagnetic fields to be dissipated completely or deflected into space.

Hotter plasmas, while dense, don't appear immediately practical as a defensive shield because of destructive temperatures and high power requirements. In theory, cold plasmas can be made denser, but like their hotter kin will demand more power. Energy availability and weight --- the larger the required wattage, the heavier the equipment --- would remain thorny issues.

"In theory, a plasma could deflect a particle beam or laser attack," Laroussi says. "It depends on what you're shooting at it and how high you can tune the plasma frequency. That doesn't mean it's easy or practically achievable, particularly with a cold plasma. It's a tough requirement to meet at present."

Cloaking mirrors
A nearer-term application is cloaking. With the proper adjustments, a plasma can be made into a kind of energy mirror, reflecting back or away incoming electromagnetic waves, such as those emitted from ground-based radars. In essence, any spacecraft outfitted with this kind of plasma field would be completely cloaked from the probing attentions of radar operators.

"The idea is to deflect or absorb the energy completely," Laroussi said. "If you absorb the energy --- completely dissipating it within the plasma --- the radar doesn't see anything. Nothing reflects back."

Light but potent
Lofting payloads into space must currently observe one of the Space Age's key commandants: Make nothing so heavy that it must cost much to launch.

Any on-board plasma-generation equipment would therefore have to be small and lightweight. Laroussi's gear seems to fit the bill -- compact enough to save on weight, yet powerful enough to produce the necessary plasma volume.

But don't expect completely impervious shields anytime soon. Any number of technical issues remains to be solved, not the least of which is exactly how to make cold plasmas dense enough to withstand attack. The ultimate --- protection against projectiles or lasers --- is likely decades away, at best.

"Ablative shields made of solid material might work," said the Air Force's Barker. "A portion of the solid would be converted to plasma [when hit]. But In a strict sense, I don't consider that plasma shielding."

The Star Wars stuff
Less immediately space-like, but no less practical, are biological applications. Cold plasmas allow for rapid decontamination of clothing, equipment or personal gear. In disrupting the integrity of cell membranes, the plasmas appear to offer a rapid, simple and inexpensive means of destroying even the hardiest bacterial spores. At present, sterilization time can run hours; use of a cold plasma could sanitize in mere minutes.

End-on view of a cold plasma inside a glass cylinder. This particular variety can be used to break down toxic gases into harmless constituents. The apparent "steering wheel" is an optical by-product of the cylinder's shape and the way the plasma is generated.

Should this application pan out, it could offer to hospitals and armies alike a safe and reliable way to counteract potential health hazards, either those posed by disease or in combat. Likewise, exobiologists might rest easy knowing that cold plasmas could remove the potential threat of contamination from collected interplanetary samples returned to Earth's surface.

Still, it's hard to vanquish all the Sci-Fi combat scenarios. Plasmas may be one of the best defensive options as offensive capabilities continue a rapid and relentless advance.

"This Star Wars stuff is coming," said Igor Alexeff. "Laser and high-power microwave weapons are on the way; they're almost here. Lasers are fierce weapons. To protect against them, you'd need a very dense plasma, almost a solid. But a good cold plasma could really help out by reflecting or absorbing energy from a microwave-powered war weapon."